Description of problem:
I was doing nothing special.

I enabled SELINUX lately and I saw the side effect that KDM offers a different default than it used to (plasma) when SELINUX was disabled.

This might be the reason.
SELinux is preventing /usr/bin/kdm from 'write' accesses on the file .dmrc.

*****  Plugin catchall (100. confidence) suggests   **************************

If you believe that kdm should be allowed write access on the .dmrc file by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# grep kdm /var/log/audit/audit.log | audit2allow -M mypol
# semodule -i mypol.pp

Additional Information:
Source Context                system_u:system_r:xdm_t:s0-s0:c0.c1023
Target Context                system_u:object_r:svirt_sandbox_file_t:s0
Target Objects                .dmrc [ file ]
Source                        kdm
Source Path                   /usr/bin/kdm
Port                          <Unknown>
Host                          (removed)
Source RPM Packages           kdm-4.11.22-2.fc23.x86_64
Target RPM Packages           
Policy RPM                    selinux-policy-3.13.1-158.fc23.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     (removed)
Platform                      Linux (removed) 4.2.8-300.fc23.x86_64 #1 SMP Tue
                              Dec 15 16:49:06 UTC 2015 x86_64 x86_64
Alert Count                   9
First Seen                    2016-01-07 08:11:36 CET
Last Seen                     2016-01-08 00:28:16 CET
Local ID                      1465764b-3f59-4846-9467-e457588b46a3

Raw Audit Messages
type=AVC msg=audit(1452209296.647:298): avc:  denied  { write } for  pid=9065 comm="kdm" name=".dmrc" dev="dm-7" ino=18087947 scontext=system_u:system_r:xdm_t:s0-s0:c0.c1023 tcontext=system_u:object_r:svirt_sandbox_file_t:s0 tclass=file permissive=0


type=SYSCALL msg=audit(1452209296.647:298): arch=x86_64 syscall=open success=no exit=EACCES a0=565183721e12 a1=a41 a2=180 a3=12 items=0 ppid=8940 pid=9065 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000 fsuid=1000 egid=1000 sgid=1000 fsgid=1000 tty=(none) ses=3 comm=kdm exe=/usr/bin/kdm subj=system_u:system_r:xdm_t:s0-s0:c0.c1023 key=(null)

Hash: kdm,xdm_t,svirt_sandbox_file_t,file,write

Version-Release number of selected component:
selinux-policy-3.13.1-158.fc23.noarch

Additional info:
reporter:       libreport-2.6.3
hashmarkername: setroubleshoot
kernel:         4.2.8-300.fc23.x86_64
type:           libreport